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  • Find the intervals in which the function   is (i)

Find the intervals in which the function f\left ( x \right )= -2x^{3}-9x^{2}-12x+1  is
(i) Strictly increasing (ii) Strictly decreasing

 

 

 

 
 
 
 
 

Answers (1)

given f\left ( x \right )= 2x^{3}-9x^{2}-12x+1
\rightarrow {f}'\left ( x \right )= -6\left ( x+1 \right )\left ( x+2 \right )= 0
\therefore x= -1,2

Interval sign of f(x)

f(x) is strictly
\left ( -\infty ,-2 \right ) Negative Decreasing
\left ( -2 ,-1 \right )  Positive  Increasing
\left ( -1 ,\infty \right ) Negative Decresing


so clearly f(x) is stricly decreasing in \left ( -\infty ,-2 \right )\cup \left ( -1,\infty \right ) and stricly increasing in \left ( -2 ,-1 \right ) .

Posted by

Ravindra Pindel

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